The present invention relates to a process for forming an ultrafine pattern by a combination of selective irradiation, deposition and etching. More particularly, the invention relates to a process for forming an ultrafine pattern suitable for the production of high-density integrated circuits.
Photolithography has commonly been used for formation of a patterned thin layer on the surface of a substrate. Photolithography for the formation of a pattern composed of, for example, a silicon dioxide film on a substrate in the form of, for example, a silicon wafer ordinarily includes steps of:
(a) coating a photoresist film on the substrate, PA0 (b) superposing a mask on the photoresist film and exposing the photoresist film through the mask to light emitted from an ultra-high pressure mercury lamp, etc. to print the pattern of the mask on the photoresist film, PA0 (c) removing the uncured photoresist film on the unexposed areas, PA0 (d) etching the silicon dioxide film, and PA0 (e) removing the photoresist film.
Apart from the above-described steps, photolithography involves steps of preparing a mask to be used in the step (b) above. The step (b) is frequently carried out by irradiation with X-rays, etc. The above-described conventional processes are, however, accompanied by the disadvantages that the pattern-formation processes require many steps, including the preparation of a mask, and much difficulty is encountered in forming an ultrafine pattern of submicron dimensions. Moreover, although extensive development efforts regarding the formation of fine patterns by photolithographic techniques have hitherto been made, the patterns obtained by the conventional processes have a lower dimensional limit of about 0.1 .mu.m.
In order to form a finer pattern, there has recently been proposed a process in which radiation condensed into a narrow beam is selectively irradiated onto the substrate, and then another material is deposited on the substrate to form a fine pattern. This process is based on the principle that stable absorption sites for the material to be deposited are formed by the radiation and that the deposited and heated atoms move on the surface of the substrate to the stable adsorption sites. As a result, this process cannot be applied to cases where the materials to be deposited are reactive with the substrate.